Motor vehicle internal combustion engines with turbochargers include a compressor for the pressure charging of a gas flow in combustion chambers of the internal combustion engine. In the case of excessive pressure innovations or pressure conditions and/or insufficient gas flows, undesirable backflows against the conveying direction of the compressor can occur, the so-called surging.
For this reason, so-called steady surge limit lines are preset according to internal company practice which assign the current gas flows a maximum permissible pressure ratio each. The compressor is then controlled based on this steady surge limit line.
In the case of unsteady operation or a change of the gas flow, this is not optimal. If the gas flow diminishes, the compressor does not follow that immediately but owing to the mechanical inertia of the turbocharger, the inertia, in particular dead time, of its control and flow-mechanical inertias only with a delay. In the case of a diminishing gas flow this can thus lead to a pressure ratio on the compressor that is too high and consequently to undesirable surging.
If this is to be excluded, the surge limit line has to be restrictively preset accordingly. Because of this the efficiency of the compressor in steady operation deteriorates however. This is true more so in unsteady operation upon an increase of the gas flow in which the inertia explained above conversely delay an actually permissible pressure ratio increase and thus a more efficient operation of the compressor.